She added: "The Government's plan for the Thames Gateway include looking at options for a new crossing.

"This is an innovative proposal, which could also have benefits for our determination to tackle climate change. I hope people will let us know what they think of the idea."

Metrotidal Ltd said the tunnel would be formed by immersing concrete tubes within a trench dredged across the Thames.

Land would be reclaimed off Canvey Island, a lagoon created on the Kent side of the river and a flood barrier installed between the two.

The plans also include a new rail route for the Thames Gateway that would link into London's Cross Rail network.

Rail orbital

The crossing would ease congestion on the M25 at the Dartford Crossing, according to Metrotidal Ltd.

Consortium director, Mark Willingale, said: "We propose to fund the tunnel by combining the emerging Government flood defence budget with wholly private-sector funding for the tunnel and tidal power plant.

"A new road connection from the A130 and A13 in Essex to the A289 and M2 in Kent will create a new road orbital system for the whole Thames Gateway region.

"Similarly, a new twin-track rail connection from Wickford and Pitsea in Essex to Rochester and Ebbsfleet in Kent will create a new rail orbital for Thames Gateway that links the eastern limbs of Cross Rail - the new cross London rail."